Ammonia Refrigerant Facts: Anesi Gas Absorption Heat Pumps

Ammonia in Large Industry

Ammonia has been used as a refrigerant since the 1850s and is widely used within the industries of agriculture, manufacturing, food and beverage, pharmaceuticals, refrigeration, wastewater treatment, water purification, and many others. Ammonia is transported in large quantities for these industrial applications often as a liquefied, compressed gas without water – known as “anhydrous ammonia”.  

Natural Ammonia

Ammonia exists naturally in the environment and is an important part of the nitrogen cycle.  Since nitrogen is the most abundant gas in Earth’s atmosphere, the cycle of repetitive processes to move it from the atmosphere to the Earth and back again to the atmosphere is part of life’s delicate balance. While nitrogen is in a gaseous form it cannot be utilized by plants. During the mineralization stage of the nitrogen cycle, nitrogen in the soil becomes a different form of nitrogen, known as ammonia (NH3).  The reaction with the water in the soil converts ammonia to ammonium (NH4) and in this form, it becomes available to plants as a fertilizer.

Why is Ammonia Used as a Refrigerant?

The American Society of Heating, Refrigerating and Air-Conditioning Engineering (ASHRAE) provides a uniform system for classifying refrigerants.  When ammonia is used as a refrigerant, it is known as R717 and classified within Inorganic Compounds. Ammonia is a common and preferred refrigerant in industrial applications because it is highly energy efficient, has a smaller heat transfer area requirement than chemical refrigerants, and is environmentally friendly with zero ozone depletion potential (ODP) and zero global warming potential (GWP).  Ammonia-water absorption heat pumps have been very widely and very safely used in multiple residential and commercial applications for over 70 years. The most common uses include space heating and cooling, water heating, and inside refrigerators for RVs and motel rooms. 

How is Ammonia Used in the Anesi Comfort System?

The Anesi gas absorption heat pump (GHP), the heating appliance within the Anesi Comfort System, contains a sealed ammonia-water absorption system.  This sealed system is designed for a low-refrigerant charge and contains approximately 12 lb. of ammonia and an approximately equivalent amount of water.  During the heat pump cycle, ammonia is separated from the water via a thermally driven process. The purified ammonia gas then circulates through an evaporator coil to capture additional heat from ambient air.  This ammonia is recombined with the water in an exothermic reaction, giving off heat which is captured by the GHP heat exchanger system and combined with the heat of fuel combustion.   This absorption cycle continuously repeats within the sealed system, producing the heat that is transferred indoors via a water and food-grade propylene glycol heat exchange fluid.  The building is warmed by this separate hydronic loop that does not contain ammonia.

What are the HVAC industry standards that guide the use of ammonia in appliances?

IIAR Standard 2 guides the safe usage of ammonia within residential and commercial HVAC systems.  An important requirement within this standard stipulates the ammonia charge within a piece of equipment should not exceed 22 lb. when located in an adjacent outdoor location.  The Anesi GHP has a 12 lb. ammonia charge within the sealed system.

What Safeguards Are in Place Within the Anesi Comfort System?

The Anesi GHP design has several embedded safety measures focusing on the refrigerant sealed system. These measures are intended to avoid any rapid release of refrigerant. It is important to remember two things – the GHP is located outdoors, and ammonia gas will quickly rise and dissipate if released outside since its density is much lower than air. The following are mechanical safeguards related to the ammonia refrigerant:

• Pressure relief valve – if the internal system pressure reaches a predefined threshold a valve will automatically open to reduce the pressure, resulting in the venting of a small portion of refrigerant vapor into the outside air.
• Diverting shield at overpressure point – the system has a steel shield at the point where overpressure would be vented, to mitigate the risk of refrigerant venting into the eyes or face of a contractor working on the system.
• Cabinetry to shield/vent – all the cabinetry surrounding the Anesi GHP sealed system is designed for safety in the unlikely release of any ammonia from the sealed system.  Vapor ammonia will rise and dissipate through the cabinetry vents. Aqueous ammonia leaks will drip into the base pan where they can be washed away with water.
• Corrosion proof system components – the GHP is designed with materials resistant to ammonia exposure eliminating concerns about corrosion and system degradation.

The following are electrical safeguards included as part of the monitoring system:

• Sealed System High Pressure – if the system pressure approaches 400 PSI, the sensor modulates (reduces) combustion.  Power to the gas valve is interrupted and the gas is turned off if the pressure exceeds 400 PSI.
• High Temperature – if the desorber temperature approaches 375 degrees, the sensor modulates (reduces) combustion.  Power to the gas valve is interrupted and the gas is turned off if the temperature exceeds 375 degrees.
• Air Pressure Switch – if the switch detects unusual or no air flow, the burner is prevented from lighting.

What Equipment Tests Are Performed at the Factory?

Stringent leak testing is performed on every GHP at various production stages at the Stone Mountain Technologies, Inc. factory.  Individual heat exchangers and the entire sealed system are pressure tested to 500 psi using air, and then to 100 psi using a very small molecule leak detection gas.  Prior to shipping, every GHP must undergo a comprehensive end-of-line operating test.

Common Ammonia Exposures

Ammonia occurs naturally in the environment and humans are exposed to low levels on a regular basis.  Pet urine, garden fertilizer, and household cleaners are just some examples. Even your food contains some amount of ammonia – especially if you live in Finland and enjoy the salty licorice salmiakki.  Farmers may experience higher exposure levels when applying fertilizers to fields or within barns and poultry houses with high quantities of manure.  The human body, through the urea cycle, prevents ammonia build up by converting ammonia into urea and excreting that through urine.

Harmful Exposures and Safety Measures Because ammonia can be dangerous at higher levels of exposure, workplace and environmental limits exist.  Ammonia has a strong pungent odor that can be detected by the human nose at levels well below any dangerous concentration.  Even at very small exposures the inclination is for humans to turn and walk or run away from the smell. This self-alarming reaction significantly reduces the chances of extended and dangerous exposures to high concentrations of ammonia, especially when outdoors.  Measured in parts per million (ppm), these exposure levels and outcomes are meant to inform and guide all activities when ammonia is present.

Depending on the target to be protected, many organizations publish exposure limits and require compliance.  This includes the Occupational Safety and Health Administration (OSHA), the International Institute of Ammonia Refrigeration (IIAR), the National Institute for Occupational Safety and Health (NIOSH), the American Industrial Hygiene Association (AIHA), and the Centers for Disease Control (CDC), among others.  The Environmental Protection Agency (EPA) has a notification requirement under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) for ammonia releases of 100 lbs or more. It is important to remember that all ammonia within the Anesi gas absorption heat pump is within a sealed system and located outside of the building.

In addition to the safety engineered into the Anesi GHP sealed system, there are several suggested safety measures for contractors who may need to work on recharging the system:

• Familiarize yourself with basic ammonia safety procedures provided through ASHRAE and IIAR.
• Always wear gloves to protect hands/skin from unintended exposure.  Any skin exposure should be washed immediately in warm soapy water.
• Always wear eye protection to avoid exposure of refrigerant solution (aqueous) or gaseous ammonia (anhydrous) to the eyes.
• Use appropriate ammonia-rated tools and supplies to avoid leaks and corrosion.